Ok then, lets give the 450 NE the benefit of the doubt and assume that it delivered the claimed ballistics of a 480 gn bullet at 2150 fps.
This gave it an energy level of 4930 ft lbs.

The 458 Win factory load was tested independently for Rifleman magazine in 1961 and was credited with 2087 fps for the 500 gn bullet in a 25 inch barrel, and, that reading was taken 20 feet from the muzzle.

Seeing that we are using an "assumed" velocity for the 450 NE it would I think be fair to also assume that an extra 13 fps could be added to the 458 WIN velocity if it was taken at the muzzle, and this would give the 458 an "assumed" speed of 2100 fps or somewhere very close to that figure.

That would have given the 458 Win Mag an energy of 4895 ft lbs compared to the 4930 ft lbs for the 450 NE.

No, the 458 may not have equaled the 450 NE in those early days but it achieved better than 99%!!!!!

99+ PERCENT!

And this with a heavier bullet!

IMO the 458 Win Mag was given a severe flogging by a few people quite some time back and while it was down, plenty of bystanders have been slipping the boot in ever since!